A study is proposed to determine the relationship, if any, between frequent habitual use of marijuana, alone and with tobacco, and the presence of respiratory symptoms and/or functional respiratory impairment. The study group will consist of a convenience sample of 400 individuals over 25 years of age who are long-term, heavy smokers of marijuana (15 marijuana cigarettes/week, or the equivalent, for 5 yrs.) and are either regular tobacco smokers (16 tobacco cigarettes/day for 5 yrs.) or non-tobacco smokers. This group will undergo 1) a detailed respiratory and drug use questionnaire to elicit further information concerning marijuana and tobacco smoking habits and other drug use, the presence of other risk factors for lung disease and the presence of respiratory symptoms; 2) analyses of blood specimens for Delta 9-THC metabolites by radioimmunoassay and for cotinine to validate responses concerning marijuana and tobacco use; and 3) a battery of pulmonary function tests, including tests which are believed to be sensitive indicators of early respiratory disease. These questionnaire responses and pulmonary function test results willbe compared with those obtained in a control group of individuals who will be group-matched to the marijuana smokers for the distribution of age, sex and tobacco smoking history by computer-selection from among 15,000 residents of the greater Los Angeles area administered the same questionnaire and lung function tests as part of an on-going population study of chronic obstructive lung disease. In addition, a selected subset of 40 heavy smokers of marijuana (20 of marijuana alone and 20 of marijuana with tobacco) will be examined by fiberoptic bronchoscopy with tracheobronchial mucosal biopsy, bronchial brushings and bronchial lavage to harvest alveolar macrophages; these studies will permit detailed examination of bronchial epithelial histopathology and alveolar macrophage ultrastructure, elemental content and function. these findings will be compared with the known tracheobronchial epithelial histology in non-smokers of either marijuana or tobacco and in smokers of tobacco alone and with the results of alveolar macrophage studies previously performed in the same laboratory in non-smokers of marijuana, including smokers and non-smokers of tobacco.